1. Field of the Invention:
The present invention relates to a geomagnetic sensor having a dip angle detection function and a dip angle detection method therefor, and more particularly, to a geomagnetic sensor having a two-axis fluxgate sensor and which is for detecting a current dip angle and a dip angle detection method therefor.
2. Description of the Related Art
A geomagnetic sensor is a device that measures the intensity and orientation of the geomagnetism that human beings cannot feel, and, in particular, a geomagnetic sensor using fluxgates is referred to as a fluxgate-type geomagnetic sensor.
That is, a fluxgate-type geomagnetic sensor refers to a device using a magnetic core of high-permeability material, such as permalloy, that measures the magnitude and direction of an external magnetic field by applying an excited magnetic field by use of a driving coil and measuring a secondary harmonic component proportional to the external magnetic field by use of the magnetic saturation and non-linear magnetic characteristics of the magnetic core.
Such a fluxgate-type geomagnetic sensor was developed in the late 1930s, and has an advantage of good sensitivity, reasonable price, and relatively small size, compared to the other types of geomagneticsensors. Further, the fluxgate-type geomagnetic sensor has another advantage of low power consumption and long-term stability of output signals, so it is most widely used for general industries and military equipment, ranging from detection of weak magnetic field and measurement of the absolute orientation of the Earth for ore exploitation, target detection, artificial satellite posture control, and space probe, and one continues to carry out research on improvements to its performance.
In particular, as Micro Electro-Mechanical system (MEMS) technologies are being gradually developed, there is a desire to develop low power consumption-type miniature fluxgate sensors by using the technologies.
FIG. 1 is a block diagram schematically showing a general structure of such a geomagnetic sensor. In FIG. 1, a geomagnetic sensor 200 has a driving signal generator 110, a two-axis fluxgate sensor 120, a signal processor 130, a controller 140, a memory 150, and a rotation angle measurement part 160.
The driving signal generator 110 applies an electric signal enabling the two-axis fluxgate sensor 120 to be driven. Such an electric signal are pulse waves or converted pulse waves.
Further, the two-axis fluxgate sensor 120 includes two fluxgates perpendicular to each other. Further, each fluxgate has a magnetic core in a rectangular ring or a bar shape, and a driving and a detection coil wound around the magnetic core. The driving coil receives an electric signal outputted from the driving signal generator 110 and excites the magnetic core, and the detection coil detects electromotive force induced by a magnetic field generated by the activation of the driving coil.
On the other hand, if the detection coil detects a voltage proportional to the intensity of an external magnetic field, the signal processor 130 deals with the voltage in a series of processes such as amplification, chopping, and so on, and outputs corresponding voltages to the respective axes.
The rotation angle measurement part 160 measures the gravitational acceleration of the geomagnetic sensor 200 to calculate a pitch angle and a roll angle. The rotation angle measurement part 160 can be implemented with two acceleration sensors perpendicular to each other, such as a two-axis fluxgate sensor 120. The pitch angle refers to a rotation angle measured in case of rotating one of two perpendicular axes with respect to the other axis wherein the two axes are perpendicular to each other with respect to the center of the geomagnetic sensor 200 on the plane on which the geomagnetic sensor is placed. The roll angle refers to a rotation angle measured in case of rotation with respect to the other axis
In general, the rotation angle measurement part 160 having a weight of certain mass enables one to visually or electrically check the movement of the weight due to gravity through an angle gauge, ruler, or indication needle so that the pitch and roll angles can be measured. The pitch and roll angles measured by the rotation angle measurement part 160 are stored in the memory 150.
Further, the controller 140 controls the normalization of the X-axis and Y-axis output voltages of the signal processor 130, the calculations of the azimuth of the geomagnetic sensor 200 by use of the pitch angle, roll angle, and current dip angle that have been measured by the rotation angle measurement part 160, and the indication of the azimuth. The dip angle is one of the three components (deflection angle, dip angle, and horizontal component) of the geomagnetic field, and refers to an angle formed between a magnetic needle and a horizontal plane when leaving the magnetic needle freely rotating vertical to the horizontal plane. The Republic of Korea has the dip angle of about 50° to 60°.
In related art devices, the azimuth is calculated with an input of a constant set for a dip angle value depending upon an area or with an input of the dip angle value from an external device such as the GPS. However, the use of dip angle values set depending upon areas causes problems of inputting a compensated value for a different area and of using an erroneous dip angle under environments in which the intensity of the geomagnetic field is varying even in the same area. Further, in case of inputting a dip angle from an external device such as GPS, more devices are needed for communicating with the external device, which causes a problem of increasing the size and manufacturing cost of a geomagnetic sensor.